please tell me what to do

Big Hug. It is normal to feel hurt when someone does this to you. Expect the feelings you have and accept them and accept the fact they will recede in time.
Confusion, anger, grief (at losing a friend), questioning (why?), and many other mixed emotions are normal and are a natural part of relationships that go bad.
You need to balance the positives and minuses, don't just look at the negative side of your life but balance this with all the positives - you have none? How about your health, you have somewhere to live and you have food, you also have other friends or acquaintances. Look at your life as a whole and see the "someone" as only a part of your whole - and a small part at that. You know that if you never speak to this person again it will not matter to you in 1, 3 or 5 years down the track.

Learn from the experience - why do you think the "someone" did this? Hey! is it justified, really? Does the truth hurt or was it an unreasonable thing for them to do? Breaking up is hard for both people and how it was done may have hurt you dearly, but perhaps in the stress the other person did not do it nicely.
Also it is much better to find out now than after you perhaps married or had children - a lucky escape? yes, I think so.
You had a life before this person and will continue to do so - so keep on living it and wait for Mr Right to come along. Take this time to look at your life and where it is going. What do you really want to do, what would you like to do and how can you do it. Now could be the time to make the changes you have thought about but were hesitant to commit to. Speak to your mum, she will understand - or perhaps an auntie or other older trusted friend. Are you still at school? a teacher or school councellor may be able to offer advice on how to follow your dreams.
Do not binge eat or look for someone else just to get back at them. Respect yourself and know that you deserve more. Try and be nice to those around you and be aware you may not be feeling your normal happy self fo a while. If you need to apologise for your behaviour to someone then go and tell them you are sorry - you are going through a tough time and didn't mean to react the way you did.
Do not shut yourself off from the world - life will go in if you are there or not - so be there and enjoy your newfound freedom. Visit friends, talk to the elderly - they have some great stories and will appreciate the company. Take time to gather your thoughts (write them down if it helps) and become a better person from having gone through what you have

Take care
Huge hug